Following your boat tour, head towards Dolmabahce, the last home of the Sultan before the dissolution of the Ottoman Empire after the First World War. On display you will find extravagant chandeliers, gold leaf ceilings and interesting architectural trends.
If wandering around Istanbul for three days has left you feeling like you need some rest, check out the Turkish bath houses, where a local scrub down will easily recharge your batteries on your fourth day. If that's not your thing, you may try sitting in the tea shops atop Camlica Hill, which has a fantastic view of the Bosforous and the Golden Horn, allowing you to also be at one with mother nature in one of the world's busiest cities.
Taking a tour of Istiklal street may also be an option, as well as an introduction to another part of the city. Some landmarks include the Anthony of Saint Padua church, the Galata Whirling Derswish museum, the Flower Passage and French street.
If you decided to spend your first couple of days in Sultanahmet, then your trip is drawing to a close. If not, however, you may have time to squeeze in such delights as a visit to the Prince's Islands, to which shamed princes used to be exiled but are these days home to magnificent old mansions among spacious avenues. Motor transport is banned on the island, therefore the only way around is on foot or by using the local, electric powered vehicles. Make sure to include a trip to the seaside and take a last glance at Istanbul!